The present invention relates to a rear axle suspension, and more particularly, to a motor vehicle rear axle suspension having an inherently stiff axle guide member with an axle tube which extends transversely to the direction of travel and at each of the two ends of which a wheel is mounted. The axle guide member is supported on a vehicle body in the region of each of the two axle tube ends by a respective bearing spring and is articulated on the body by a universal joint in the region of the central longitudinal plane of the vehicle, in front of the wheel rotation axis, referring to the forward direction of travel. The suspension has a lateral guide linkage which consists of two individual links and in which the one link is articulately supported, at its one end in the region near the wheel, on one end of the axle tube, and the other link is articulately supported, by its end in the region near the wheel, on the other end of the axle tube. The other two ends of the two links are articulated to a coupling device which permits equalizing movements of the links in the transverse direction and which is fastened to the vehicle body in the region of the central longitudinal plane of the vehicle. The fastening point of the coupling device lays behind the points of support of the links on the axle tube, referring to the forward direction of travel.
In a suspension described in FR-OS 2 319 507, the axle guide member is formed by a straight axle tube which connects the two wheels to one another and to which is fastened a bar which in turn is articulated on the vehicle body by a universal joint in the central longitudinal plane of the vehicle. Transverse guidance is effected by a Watt linkage which is articulated on the axle tube in the region near the wheel and to the body in the region of the central longitudinal plane of the vehicle. Because the distance between the articulation point of the Watt linkage on the body and the wheel rotation axis is infinitesimal compared with the distance between the articulation point of the axle guide member on the body and the wheel rotation axis when a lateral force occurs (e.g., during cornering), the force component supported in the transverse direction at the articulation point of the bar is relatively slight compared with the force component which has to be supported in the transverse direction at the articulation point of the Watt linkage on the body.
Almost the entire transverse force is thus supported through the mounting of the Watt linkage on the body in the known suspension. Consequently, when a lateral force occurs (e.g., cornering), through the comparatively only very slight action of this lateral force, the bar can also travel only a short distance relative to a given elasticity of the bar mounting in the transverse direction. The axle thus has a slight tendency to oversteer under the action of a lateral force. Even the slightest elasticity at the mounting point of the Watt linkage on the body very considerably increases this undesirable roll steer effect of the axle under the action of a lateral force. The ability to adapt the mounting of the axle guide member and that of the Watt linkage on the body, in respect of elasticity in the transverse direction, is thus greatly restricted.
Reimpell Fahrwerktechnik: Radaufhangungen (Wheel Suspensions), p. 182 (1st Ed. 1986), describes a rear axle in which the axle tube has a configuration curved in the forward direction of travel and, in the region of the central longitudinal plane of the vehicle, is articulated to the vehicle body by a universal joint. The transverse guidance of this rear axle is effected by two tie rods which extend obliquely and each of which is articulately connected, on one hand, to the axle tube and, on the other hand, to the vehicle body.
In a rear axle described in DE-OS 27 51 997, the axle body is formed of two gear casings which are arranged in the region near the wheel and extend in the forward direction of travel. Those ends of the gear casings which lie at the front in the forward direction of travel are in each case connected by a respective tube portion to a differential situated in the region of the central longitudinal plane of the vehicle. The differential is, in turn, connected via a joint to the vehicle body. Transverse guidance of this rear axle is effected by a Watt linkage which extends substantially at the height of the axes of rotation of the wheels and the rocker of which is articulated on the vehicle body. Those ends of the links of the Watt linkage which are each remote from the rocker are articulated on a respective gear casing. Since the Watt linkage extends substantially at the height of the axes of wheel rotation, lateral guide forces, for example during cornering, are supported practically exclusively by the Watt linkage.
An object on which the present invention is based is, therefore, to provide a rear axle suspension of the aforementioned kind, with which the tendency to oversteer under the action of a lateral force can be reduced, and with which the ability to adapt the mounting of the axle guide member and that of the lateral guide linkage on the body can be improved.
The foregoing object has been achieved in accordance with the present invention by a rear axle suspension in which the axle tube has a configuration curved in the forward direction of vehicle travel, the axle tube is articulated on the vehicle body by a universal joint, and a distance between the axle tube, in a region of articulation of the axle tube on the vehicle body, and the axis of rotation of the wheel is substantially equal to a distance from the lateral guide linkage, in a region of articulation thereof on the vehicle body, to the axis of rotation of the wheel.
Because of the substantially equal distance from the axis of rotation of the wheel to the point of articulation of the axle tube, which is curved in the forward direction of travel, on the body and to the articulation of the lateral guide linkage on the body, a lateral force occurring is supported in approximately equal parts by the mounting of the axle tube on the body and by the mounting of the lateral guide linkage on the body. In relation to a given elasticity in the support of the axle tube on the body in the transverse direction, under the action of a lateral force, a greater distance is thus travelled, so that the tendency to oversteer is reduced.
Furthermore, because of the equal division of the transverse forces now made between the two mounting points (axle tube and lateral guide linkage) on the body, the elasticities in the two mountings can be adapted to one another in an optimum manner in respect of neutral steering behavior under the action of a lateral force.
The rear axle suspension according to the present invention also has the advantage that only little installation space is required but sufficient space is nevertheless always still available to receive a lowered part of the body such as, for example, a recess for a spare wheel or a fuel tank.
With the configuration according to the present invention, a relatively great sweep of the lateral guide linkage is obtained. This has the advantage that the force level in the two links, which are subjected only to-tension and compression, is reduced by this increased sweep.